1. Field of the Invention
The invention relates to a rotor of a rotary electric machine, which includes a rotor core, and permanent magnets embedded near an outer periphery of the rotor core.
2. Description of Related Art
In a permanent magnet synchronous rotary electric machine in which permanent magnets are embedded inside of a rotor core, when a temperature of a rotor increases as the rotary electric machine is driven, not only does the magnetic performance decrease causing a reduction in torque and efficiency, but the permanent magnets will demagnetize when the temperature becomes high. When magnets having high coercive force are employed, the problem of demagnetization is able to be avoided, but in this case, the content percentage of heavy rare earth must be increased, which leads to a cost increase.
Therefore, various structures of the related art have been proposed to a cool rotary electric machine. For example, Japanese Patent Application Publication No. 2008-228522 (JP 2008-228522 A) describes technology that cools a rotor by discharging oil supplied from an oil supply passage formed inside of a rotating shaft, through a plurality of cooling oil passages formed inside of a rotor core. In JP 2008-228522 A, for example, a cooling oil passage that extends on a q-axis of the rotary electric machine is formed by forming slots that extend on the q-axis, offset by a span in the radial direction, in each of a plurality of magnetic steel sheets that are lined up sequentially in the axial direction.
Also, Japanese Patent Application Publication No. 2006-067777 (JP 2006-067777 A) describes technology that cools a rotor by discharging oil supplied from an oil supply passage formed inside of a rotating shaft, through a plurality of cooling oil passages formed inside of a rotor core. In JP 2006-067777 A, the cooling oil passages extend on a d-axis of a rotary electric machine. In JP 2006-067777 A, a plurality of oil passages that extend in the radial direction are lined up in the axial direction.
Japanese Patent Application Publication No. 2012-223075 (JP 2012-223075 A) describes technology in which a through-hole that extends in an axial direction is formed in a rotor core, and cooling oil is supplied from one end to the other end of the through-hole. In JP 2012-223075 A, the through-hole is formed such that a distance between the through-hole and an outer peripheral surface of the rotor core is smaller on the other end side (a downstream side of an oil flow path) than on the one end (the upstream side of the oil flow path).
However, with the technology described in JP 2008-228522 A, there is no oil passage that extends in the axial direction, so cooling tends to be uneven in the axial direction, and consequently, the rotor is unable to be efficiently cooled. In JP 2006-067777 A, a plurality of oil passages that extend in the radial direction are lined up in the axial direction, so unevenness in cooling is able to be improved somewhat compared to JP 2008-228522 A. However, in JP 2006-067777 A as well, there is no oil passage that extends in the axial direction, so unevenness in cooling in the axial direction is unable to be effectively reduced. Also, in JP 2006-067777 A, oil is discharged from a plurality of discharge ports lined up in the axial direction into a gap that is a space between the rotor and the stator. Here, the oil discharged into the gap is discharged outside from both axial ends (i.e., both ends in the axial direction) of the gap. However, in JP 2006-067777 A, oil discharged from one of the discharge ports tends to interfere with oil discharged from a discharge port in a different axial position as it proceeds to the axial end portion of the gap. In this case, the cooling medium stays in the gap for an extended period of time without reaching the axial end portion of the gap. This accumulation of oil leads to an increase in drag loss.
With the technology described in JP 2012-223075 A, oil flows through the though-hole that extends in the axial direction, so the rotor is able to be cooled all along in the axial direction. However, in JP 2012-223075 A, oil is discharged from both axial ends of the rotor toward the coil end of the stator. In other words, in JP 2012-223075 A, oil is not supplied into the gap. As a result, even though the coil of the stator is able to be cooled, the outer peripheral surface of the rotor may not be able to be sufficiently cooled. That is, no related structure is able to efficiently cool the entire rotor.